Field of the Invention
The present invention relates to a sheet feeding apparatus, an image forming apparatus, and an image forming system that accommodate and feed a transfer medium.
Description of the Related Art
An image forming apparatus that performs printing by forming an image on a transfer medium feeds the transfer medium placed on a tray of a sheet feeding apparatus. The sheet feeding apparatus may be provided inside or outside an image forming apparatus body to feed the transfer medium to the image forming apparatus.
A usable transfer medium is considered for the tray of the sheet feeding apparatus, and the tray is moved vertically by a driving motor corresponding to the usable transfer medium. According to a basic operation of the tray, the tray moves up to an upper limit to take a feedable state. In addition, the tray can be lowered such that the transfer medium can be supplied to the tray. The vertical movement of the tray is performed within a range of assumed loading amount, and is generally restricted in the case where transfer media of an amount exceeding a maximum loading amount are placed on the tray.
JP 7-239639 A discloses giving usability priority and, in replenishing a large capacity cassette with paper sheets, allowing a feeding function to operate even when the paper sheets of an amount equal to or larger than a regulated amount of loading on the tray are loaded on the tray. Specifically, in the case where the paper sheets of an amount equal to or more than the regulated amount of loading are loaded on the tray, a warning screen is displayed regardless of the size of the paper sheets by, when a tray-up switch detects the paper sheets loaded on the tray, stopping lifting of the tray by a motor, enabling feeding of the paper sheets, and, at the same time as turning on of the tray-up switch, display an error message of “please reduce the paper sheets” in the case where a tray-down switch that determines the lowest position of the tray is on.
JP 8-91593 A discloses appropriately restricting the loading by restricting the degree of descent of a sheet feeding tray at the time of loading paper sheets such that a user cannot load the paper sheets exceeding an amount corresponding to the degree of descent of the tray. Specifically, the size of the paper sheets is determined by a sheet size detection unit of a sheet feeding apparatus, a load current value of a tray lifting/lowering motor preset for the size of the paper sheets is extracted, and a current position of the sheet feeding tray is determined by an upper limit detection sensor and a lower limit detection sensor (neither illustrated) of the sheet feeding apparatus. The number of sheets remaining to be loadable and the time of movement to a maximum loading lower limit position are calculated with a prescribed formula, the tray lifting motor is caused to drive for a time extracted by the calculation, the tray is lowered and stopped, and the position is set as the lower limit position corresponding to the maximum loading number of sheets. In this way, the lower limit position of the tray can be changed for each size of the paper sheets.
By the way, generally, a loading amount limit of transfer media is often defined along with usable sizes, and transfer media of a size larger than these are not taken into consideration.
However, there is a demand for expanding the usable sizes of sheets for the sheet feeding apparatus without changing the inner configuration of the sheet feeding apparatus, and a configuration in which a long sheet of a size exceeding the usable sizes can be used is desired. However, in the case where long transfer media of a number equal to or larger than a prescribed number of sheets are loaded, the mass of the transfer media surpasses the performance of a motor provided in the sheet feeding apparatus to lift the sheet feeding tray, and thus the tray cannot be lifted. Therefore, in the case where long transfer media are loaded on the tray, the loading needs to be restricted. In order to avoid this, the power of the motor may be enhanced such that the transfer media can be loaded, but this raises the costs.